Optical compensation film and method for manufacturing the same

ABSTRACT

An optical compensation film for a liquid crystal display is provided and comprises a liquid crystal layer which is disposed on a substrate and has a plurality of first stripe-structure regions with a first thickness and a plurality of second stripe-structure regions with a second thickness, wherein each of the second stripe-structure regions is contiguous to at least one of the first stripe-structure region and the second thickness is greater than the first thickness. The method for manufacturing the optical compensation film is provided.

RELATED APPLICATIONS

This application claims priority to Taiwan Application Serial Number100124661, filed Jul. 12, 2011, which is herein incorporated byreference.

BACKGROUND

1. Technical Field

The disclosure relates to an optical compensation film and a method formanufacturing the same, and more particularly to an optical compensationfilm and an embossing method for manufacturing the same.

2. Description of Related Art

A liquid crystal display has already replaced a traditional cathode raytube (CRT) and become a mainstream display technology. The liquidcrystal display controls the penetration or shielding of light by thebirefringence of liquid crystal molecules in the liquid crystal displayto achieve the function of display. However, the liquid crystal displayhas the disadvantage of the viewing angle. Several technologies areproposed for improving the viewing angle of liquid crystal display, suchas an optical compensation film, multi-domain vertical alignment (MVA)and in-plane switching (IPS). In brief, the MVA and IPS improve theviewing angle by modifying the structure of liquid crystal displaypanel. The optical compensation film improves the viewing angle throughthe phase retardation of an optical compensation film. The opticalcompensation film can be integrated with polarizing film into a liquidcrystal display panel.

However, the conventional optical compensation film encounters theproblem of red light leakage and blue light leakage when being used witha large viewing angle. Therefore, there is a need to provide an opticalcompensation film with a different phase retardation that is capable ofcompensating different colors for alleviating the aforesaid disadvantageof the prior art.

SUMMARY

An aspect of the present invention is to provide an optical compensationfilm for improve the aforementioned problems.

In an embodiment of the present invention, the optical compensation filmcomprises a liquid crystal layer which is disposed on a substrate andhas a plurality of first stripe-structure regions with a first thicknessand a plurality of second stripe-structure regions with a secondthickness, wherein each of the second stripe-structure region iscontiguous to at least one of the first stripe-structure regions and thesecond thickness is greater than the first thickness.

In another embodiment of the present invention, the optical compensationfilm comprises a substrate, a step-like structure resin layer and aliquid crystal layer. The step-like structure resin layer is formed on asurface of the substrate and has a plurality of step-like structuresregularly arranged thereon. The liquid crystal layer is disposed on thestep-like structure resin layer and has a plurality of firststripe-structure regions with a first thickness and a plurality ofsecond stripe-structure regions with a second thickness, wherein thesecond thickness is greater than the first thickness.

According to a further aspect of the present invention, a method formanufacturing the optical compensation film is provided.

In an embodiment of the present invention, the method for manufacturingthe optical compensation film comprises the following steps. Firstly, aUV curable resin is applied on a substrate. Next, the UV curable resinis embossed to form a step-like structure resin layer comprising aplurality of step-like structures. Then, the step-like structure resinlayer is cured by UV light. Thereafter, a liquid crystal layer is formedon the step-like structure resin layer.

The forgoing presents a simplified summary of the disclosure in order toprovide a basic understanding of the present invention. This summary isnot an extensive overview of the disclosure and it does not identifykey/critical elements of the present invention or delineate the scope ofthe present invention. Its sole purpose is to present some conceptsdisclosed herein in a simplified form as a prelude to the more detaileddescription that is presented later.

Many of the attendant features will be more readily appreciated as thesame becomes better understood by reference to the following detaileddescription considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an optical compensation filmaccording to an embodiment of this invention;

FIG. 2 is a cross-sectional view of an optical compensation filmaccording to another embodiment of this invention; and

FIGS. 3A to 3C illustrates a flowchart showing a method formanufacturing the optical compensation film according to an embodimentof this invention.

DETAILED DESCRIPTION

Accordingly, an optical compensation film and a method for manufacturingthe same are provided. In the following detailed description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the disclosed embodiments.It will be apparent, however, that one or more embodiments may bepracticed without these specific details. In other instances, well-knownstructures and devices are schematically shown in order to simplify thedrawing.

FIG. 1 is a cross-sectional view of an optical compensation film 100according to an embodiment of this invention. The optical compensationfilm 100 can be used in birefringent light valve display equipment, suchas, a liquid crystal display, to improve the viewing angle, the contrastand the display quality of a display. The optical compensation film 100shown in FIG. 1 comprises a substrate 110 and a liquid crystal layer120.

The substrate 110 is used to support the liquid crystal layer 120 andprovides appropriate mechanical properties to the optical compensationfilm 100. The material of substrate 110 can be penetrated by visiblelight. The example of the material of substrate 110 can be cellulosicresin such as cellulose triacetate (TAC), polyesters, polycarbonates,polyamides, polystyrenes, acrylics, acetates and any appropriatetransparent resin. Moreover, thermoset resin and UV curable resin can beused as the material of substrate 110, such as polyurethanes, acrylicpolyurethanes, epoxy resin and silicone resin. In a preferred embodimentof the present invention, due to the consideration of polarization anddurability, the substrate 110 includes cellulose triacetate (TAC).

The liquid crystal layer 120 is disposed on the substrate 110. Theliquid crystal layer 120 has a plurality of first stripe-structureregions R1 with a first thickness d1 and a plurality of secondstripe-structure regions R2 with a second thickness d2. Each of thesecond stripe-structure regions R2 is contiguous to at least one of thefirst stripe-structure region R1 and the second thickness d2 is greaterthan the first thickness d1 as shown in FIG. 1.

In an embodiment of the present invention, the liquid crystal layer 120further comprises a plurality of third stripe-structure regions R3 witha third thickness d3, in which each of the third stripe-structure regionR3 is contiguous to the second stripe-structure region R2 and the thirdthickness d3 is greater than the second thickness d2 as shown in FIG. 1.In an embodiment of the present invention, the liquid crystal layer 120comprises three different thicknesses for three different phaseretardations.

In another embodiment of the present invention, the optical compensationfilm 100 comprises a step-like structure resin layer 111 disposed on thesubstrate 110. The step-like structure resin layer 111 comprises aplurality of step-like structures 112 with at least two steps below theliquid crystal layer 120. In an embodiment of the present invention, thestep-like structures 112 comprise an upper step 114 and a lower step 116which are below the first stripe-structure region R1 and the secondstripe-structure region R2 of the liquid crystal layer 120 respectively.In this embodiment, there is no step-like structure 112 below the thirdstripe-structure region R3 of the liquid crystal layer 120. Therefore,the third thickness d3 is greater than the second thickness d2. Thestep-like structures 112 can be regularly arranged on the substrate 110.In an embodiment of the present invention, the step-like structures 112are formed from UV curable resin, for example.

The liquid crystal layer 120 is birefringent, and thus the differentthicknesses of the liquid crystal layer 120 provide different phaseretardations to compensate lights with different wavelengths. In therelevant technology, phase retardation is represented by Δn×d, whereinΔn is a refractive index difference of the birefringent material on twoperpendicular axes, and d is an optical path. Because the lights withdifferent wavelengths have different refractive indices, and differentthicknesses of the liquid crystal layer 120 (i.e. the optical path d) ofthe present compensation film are respectively constructed for thevarious lights transmitted through the liquid crystal layer 120 in orderto enable the lights in different wavelength regions to reach similarphase retardation.

In brief, the liquid crystal layer 120 has three differentstripe-structure regions R1, R2 and R3 with three different thicknessesd1, d2 and d3 respectively. The first stripe-structure region R1 of theliquid crystal layer 120 has the smallest thickness (the first thicknessd1) and can be used to compensate the light with a shorter wavelength,for example, the blue light. The third stripe-structure region R3 of theliquid crystal layer 120 has the greatest thickness (the third thicknessd3) and can be to compensate the light with a longer wavelength, forexample, the red light. The second stripe-structure region R2 of theliquid crystal layer 120 has a medium thickness (the second thicknessd2) and can be used to compensate the light with a medium wavelength,for example, the green light. In an embodiment of the present invention,the first stripe-structure regions R1 are corresponding to blue pixelsin the liquid crystal display panel. Similarly, the secondstripe-structure regions R2 and the third stripe-structure regions R3are corresponding respectively to green pixels and red pixels in theliquid crystal display panel. A width of each of the firststripe-structure regions R1, a width of each of the secondstripe-structure regions R2 and a width of each of the third tostripe-structure regions R3 are respectively corresponded to a width ofa pixel in a liquid crystal display panel. In this embodiment, the widthof each of first stripe-structure regions R1, the width of each of thesecond stripe-structure regions R2 and the width of each of the thirdstripe-structure regions R3 are in a range from 100 microns (μm) to 400microns (μm), and preferably in a range from 200 microns (μm) to 350microns (μm).

It is known that the optical compensation film is generally designed forcompensating green light, and thus leakage of the blue light and the redlight occur in a display with a large viewing angle, which willadversely affect the display quality and the contrast of the liquidcrystal display. The optical compensation film of this present inventionhas a plurality of different stripe-structure regions to compensatelights with different wavelengths respectively so as to alleviate theaforesaid disadvantages of the prior art.

The substrate 110 can be optical isotropic or birefringent. The designof first thickness d1, the second thickness d2 and the third thicknessd3 of the liquid crystal layer 120 are affected by the different opticalproperties of substrate 110. The different thicknesses in liquid crystallayer 120 for different substrate are described as follow.

In an embodiment of the present invention, when the substrate 110 isoptically isotropic, Δn×d of the first stripe-structure regions R1, thatof the second stripe-structure regions R2 and that of the thirdstripe-structure regions R3 are about 320 nm, 340 nm and 380 nmrespectively. In a specific embodiment, the first thickness d1 of theliquid crystal layer 120 is about in a range from 2.3 to 2.4 microns(μm), and the second thickness d2 of the liquid crystal layer 120 isabout in a range from 2.4 to 2.5 microns (μm), and the third thicknessd3 of the liquid crystal layer 120 is about in a range from 2.7 to 2.8microns (μm).

In another specific embodiment, the substrate 110 is birefringent andthe Δn×d of the substrate 110 is about 100 nm. In this embodiment, thefirst thickness d1 of the liquid crystal layer 120 is about in a rangefrom 1.6 to 1.7 microns (μm), and the second thickness d2 of the liquidcrystal layer 120 is about in a range from 1.7 to 1.8 microns (μm), andthe third thickness d3 of the liquid crystal layer 120 is about in arange from 2.0 to 2.1 microns (μm) thereon.

Moreover, the liquid crystal layer 120 may have different components fordifferent types of liquid crystal display. For example, the liquidcrystal layer 120 of the optical compensation film 100 for a twistnematic or vertical alignment liquid crystal display comprises A-plateand C-plate. The aforementioned A-plate and C-plate are uniaxial opticalanisotropy; the optic axis of A-plate is parallel to the extensiondirection of the layer; and the optic axis of C-plate is vertical to theextension direction of the layer.

In another embodiment of the present invention, the optical compensationfilm 100 further comprises an alignment film 130 disposed between thesubstrate 110 and the liquid crystal layer 120 as shown in FIG. 2. Thealignment film 130 is adjacent to the liquid crystal layer 120 forproviding the directional alignment which is required by the liquidcrystal layer 120. The alignment film 130 is substantially formed alongthe surface of substrate 110, and thus the liquid crystal layer 120still has different thicknesses. The alignment layer 130 can be formedon the substrate 110 by using a process known to those skilled in theart, such as a micro-scratch alignment treatment, a rubbing treatment,photo-alignment, SiO₂ evaporation or ion-beam alignment.

According to a further aspect of the present invention, a method formanufacturing the optical compensation film is provided. A preferredembodiment of the method of the present invention is illustrated byFIGS. 3A to 3C.

FIGS. 3A to 3C illustrate the steps in a method for manufacturing theoptical compensation film according to an embodiment of the presentinvention. First, a substrate 210 is provided. Then, an UV curable resin220 is applied on the substrate 210 by a process known to those skilledin the art, such as, slit coating, roller coating or die coating, asshown in FIG. 3A. After the UV curable resin 220 is applied, the solventin the UV curable resin 220 can be optionally removed by a dryingtreatment. Before the UV curing treatment, the UV curable resin 220 hasadequate liquidity. However, the UV curable resin 220 is cured and hascertain hardness after the UV curing treatment. In a preferredembodiment of the method of the present invention, the UV curable resin220 has appropriate visible light transmittance.

After the UV curable resin 220 is applied on the substrate 210, the UVcurable resin 220 is embossed to form a step-like structure resin layer230 comprising a plurality of step-like structures 231. The embossingtreatment can be performed by using a stamp or a roller having apredetermined structure formed on the surface of the stamp or roller. Inan embodiment of the method of the present invention, the embossingtreatment is performed by using a grooved roller, for example. Thesurface of the roller is molded with a plurality of step-like structurescomprising an upper step and a lower step regularly arranged, and thestep-like structures on the roller are transferred to the UV curableresin 220 to form a plurality of step-like structures 231 regularlyarranged on the substrate 210. In brief, the protruding parts of thestep-like structure 231 on the compensation film 210 are form by theconcave parts of the step-like structures on the grooved roller, suchthat the step-like structures 231 of the step-like structure resin layer230 comprises an upper step 233 and a lower step 235, and the thicknessof the upper step 233 and the lower step 235 are different, as shown inFIG. 3B.

After the embossing treatment, the step-like structure resin layer 230is conducted by using a UV curing treatment. The wavelength of the UVlight used in the UV curing treatment and the application time of curingare adjusted for the different types of materials. After the embossingtreatment, an alignment treatment is performed on the step-likestructure resin layer 230 optionally, such as rubbing process that isknown to those skilled in the art, so as to facilitate the alignment ofthe liquid crystal molecules subsequently. In another embodiment of themethod of the present invention, after the step-like structure resinlayer 230 is cured, an alignment layer is formed on the step-likestructure resin layer 230 and an alignment treatment is conducted to thealignment layer optionally, for example, the alignment treatment isphoto alignment. The alignment layer can be formed by a process known tothose skilled in the art, such as a micro-scratch alignment treatment,SiO₂ evaporation or ion-beam alignment. In still another embodiment ofthe method of the present invention, an alignment layer is not necessaryto be formed, and the liquid crystal molecules are aligned bypredetermined alignment grooves on the step-like structure layer 230which are formed with the step-like structure layer 230 by the embossingtreatment.

After the UV curing treatment, a liquid crystal layer 240 is formed onthe step-like structure layer 230. The liquid crystal layer 240 can beformed by a process known to those skilled in the art, such as slitcoating. In an embodiment of the method of the present invention, afluid with liquid crystal molecules is coated on the step-like structurelayer 230, and then a heat treatment is performed on the liquid crystallayer 240.

According to a further another aspect of the present invention, anoptical compensation film 100 comprising a substrate 110, a step-likestructure resin layer 111 and a liquid crystal layer 120 is provided, asshown in FIG. 1. The step-like structure resin layer 111 has a pluralityof step-like structures 112 formed on a surface of the substrate 110, inwhich the step-like structures 112 are regularly arranged on thesubstrate 110 comprising an upper step 114 and a lower step 116. Theliquid crystal layer 120 is disposed on the step-like structure resinlayer 111 and has a plurality of first stripe-structure regions R1 witha first thickness d1 and a plurality of second stripe-structure regionsR2 with a second thickness d2, and the second thickness d2 is greaterthan the first thickness d1.

While the invention has been described by way of example(s) and in termsof the preferred embodiment(s), it is to be understood that theinvention is not limited thereto. On the contrary, it is intended tocover various modifications and similar arrangements and procedures, andthe scope of the appended claims therefore should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements and procedures.

1. An optical compensation film, comprising: a substrate; a liquidcrystal layer which is disposed on the substrate and has a plurality offirst stripe-structure regions with a first thickness and a plurality ofsecond stripe-structure regions with a second thickness, wherein each ofthe second stripe-structure region is contiguous to at least one of thefirst stripe-structure regions and the second thickness is greater thanthe first thickness.
 2. The optical compensation film of claim 1,wherein the liquid crystal layer has a plurality of thirdstripe-structure regions with a third thickness, and each of the thirdstripe-structure regions is contiguous to the second stripe-structureregion and the third thickness is greater than the second thickness. 3.The optical compensation film of claim 1, further comprising a step-likestructure resin layer which has a plurality of step-like structures withat least two steps and is contiguous to the liquid crystal layer.
 4. Theoptical compensation film of claim 3, wherein the step-like structuresare respectively disposed below the first stripe-structure regions andthe second stripe-structure regions.
 5. The optical compensation film ofclaim 1, further comprising an alignment film disposed between thesubstrate and the liquid crystal layer.
 6. The optical compensation filmof claim 2, wherein a width of each of the first stripe-structureregions, a width of each of the second stripe-structure regions and awidth of each of the third stripe-structure regions are respectivelycorresponding to a width of a pixel in a liquid crystal display panel.7. The optical compensation film of claim 2, wherein the substrate isbirefringent, and the first thickness is in a range from 1.6 microns(μm) to 1.7 microns (μm), and the second thickness is in a range from1.7 microns (μm) to 1.8 microns (μm), and the third thickness is in arange from 2.0 microns (μm) to 2.1 microns (μm) thereon.
 8. The opticalcompensation film of claim 2, wherein the substrate is opticallyisotropic, the first thickness is in a range from 2.3 microns (μm) to2.4 microns (μm), and the second thickness is in a range from 2.4microns (μm) to 2.5 microns (μm), and the third thickness is in therange from 2.7 microns (μm) to 2.8 microns (μm).
 9. An opticalcompensation film comprising: a substrate; a step-like structure resinlayer which is formed on a surface of the substrate and has a pluralityof step-like structures regularly arranged on the substrate; and aliquid crystal layer which is disposed on the step-like structure resinlayer and has a plurality of first stripe-structure regions with a firstthickness and a plurality of second stripe-structure regions with asecond thickness, wherein the second thickness is greater than the firstthickness.
 10. A method of manufacturing an optical compensation film,the method comprising: applying an UV curable resin on a substrate;embossing the UV curable resin to form a step-like structure resin layercomprising a plurality of step-like structures; curing the step-likestructure resin layer by UV light; and forming a liquid crystal layer onthe step-like structure layer which has been cured.